Polycrystalline diamond (“PCD”) compacts are used in a variety of mechanical applications, for example in material removal operations, as bearing surfaces, and in wire-drawing operations. PCD compacts are often used in the petroleum industry in the removal of material in downhole drilling. The PCD compacts are formed as cutting elements, a number of which are attached to drill bits, for example, roller-cone drill bits and fixed-cutting element drill bits.
PCD cutting elements typically include a superabrasive diamond layer, referred to as a polycrystalline diamond body, which is attached to a substrate. The polycrystalline diamond body may be formed in a high pressure high temperature (HPHT) process, in which diamond grains are held at pressures and temperatures to cause the diamond particles bond to one another.
As is conventionally known, the diamond particles are introduced to the HPHT process in the presence of a catalyst material that, when subjected to the conditions of the HPHT process, promotes formation of interparticle diamond bonds. The catalyst material may be embedded in a substrate, for example, a cemented tungsten carbide substrate having cobalt. The catalyst material may infiltrate the diamond particles from the substrate. Following the HPHT process, the diamond particles are sintered to one another and may be attached to the substrate.
While the catalyst material promotes formation of the inter-diamond bonds during the HPHT process, the presence of the catalyst material in the sintered diamond body after the completion of the HPHT process may also reduce the stability of the polycrystalline diamond body at elevated temperatures. Some of the diamond grains may undergo a back-conversion to a softer non-diamond form of carbon (for example, graphite or amorphous carbon) at elevated temperatures. Further, mismatch of the thermal expansion of the materials may induce stress into the diamond lattice causing microcracks in the diamond body. Back-conversion of diamond and stress induced by the mismatch of thermal expansion of the materials may contribute to a decrease in the toughness, abrasion resistance, and/or thermal stability of the PCD cutting elements during operation.
Accordingly, polycrystalline diamond cutting elements that have improved thermal stability may be desired.